Secondary batteries called lithium ion batteries, currently attracting attention, can broadly be classified into two categories of so called lithium ION secondary batteries and lithium METAL secondary batteries. The lithium METAL secondary batteries utilize precipitation and dissolution of lithium for the operation. Besides, the lithium ION secondary batteries utilize storage and release of lithium in the charge-discharge reaction. These batteries both can provide large energy densities as compared with lead batteries or nickel-cadmium batteries. By making use of this characteristic, in recent years, these batteries have been widely distributed as power supplies for portable electronic equipment such as camera-integrated VTR's (video tape recorders), mobile telephones, and notebook computers. Under the circumstance, the development of lithium ion secondary batteries is progressed, particularly for providing lightweight products with achieving high energy densities. Furthermore, there is a strong demand for size reduction, weight reduction, service life prolongation, and safety enhancement.
Regarding a liquid electrolyte for lithium ion secondary batteries or lithium metal secondary batteries (hereinafter, these may be collectively referred to simply as a lithium ion secondary battery), in order to realize high electric conductivity and potential stability, a particular combination of materials has widely been employed. That is, a carbonic acid ester-based solvent such as propylene carbonate or diethyl carbonate is employed, in combination with an electrolyte salt such as lithium hexafluorophosphate.
As an example of improving the liquid electrolyte in terms of the components thereof, particular cyclic compounds have been applied in order to suppress an increase in the internal resistance at the time of a high temperature (80° C.) (see Patent Literature 1). Furthermore, in a specialized cell having a film of polyvinylidene fluoride formed on the electrodes, gas generation at the time of discharge can purportedly be suppressed by adding an acid anhydride to the liquid electrolyte (see Patent Literature 2).